17β-hydroxysteroid dehydrogenase 3 (17β-HSD3) is an essential enzyme in the biosynthesis of testosterone. It catalyzes the reduction of androstenedione, a weakly active androgen produced by the adrenal glands, to testosterone. Inano et al., Steroids, 48, 1-26, (1986) and Luu-The et al., J. Steroid Biochem. Mol. Biol., 55, 581-587 (1995). 17β-HSD3 is expressed predominately in the adult testes and to a lesser extent in seminal vesicles and prostate tissue, an expression pattern consistent with an enzyme involved in both gonadal and peripheral target tissue androgen biosynthesis. 17β-HSD3 is responsible for the synthesis of about 60% of all active androgens in men. Labrie, Mol. Cell. Endocrinol. 78, C113-C118 (1991). The development and progression of hormone sensitive diseases, e.g., prostate cancer, is stimulated by androgens such as testosterone. Inhibition of 17β-HSD3 therefore provides a novel means to disrupt testosterone biosynthesis for the treatment of androgen-associated diseases. Van Weerden et al., J. Steroid Biochem. Mol. Biol., 20, 903-907 (1990) and Liu et al., J. Clin. Endocrinol., 77, 1472-1478 (1993).
Current pharmacological treatments to prevent androgen action in androgen-associated diseases such as prostate cancer are centered on the combined use of luteinizing hormone releasing hormone (LHRH) analogues with androgen receptor antagonists (“anti-androgens”). Labrie et al., Endocr.-Relat. Cancer, 3, 243-278 (1996); Gheiler et al., World J. Urol., 18, 190-193 (2000); and Simard, et al., J. Urol., 49, 580-586 (1997). LHRH analogues interfere with central nervous system feedback mechanisms to suppress testosterone biosynthesis in the testes to produce chemical castration. However, it is estimated that up to 50% of testosterone levels remain within prostate tissue following chemical or surgical castration indicating the existence of alternate routes of testosterone biosynthesis independent of the testes. Anti-androgens are used to block the action of this remaining testosterone in prostate cancer cells by antagonizing hormone function at the level of receptor binding. Although the combined use of LHRH analogues with anti-androgens has shown success in the management of prostate cancer, these responses are largely restricted to advanced metastatic disease. Further, patients receiving these treatments ultimately become refractory and progress to a more aggressive, hormone-independent state for which there is no effective therapy.
Inhibitors of 17β-HSD3 have been described in the art. See, e.g., Pittaway, Contraception, 27, 431 (1983); Labrie et al., WO99/46279; Maltais et al., J. Med. Chem., 45, 640-653 (2002); and Guzi et al., WO03/022835. There remains a need for potent, selective inhibitors of 17β-HSD3 with improved pharmacological properties, physical properties and side effect profiles.
The compounds of the present invention are inhibitors of 17β-HSD3, and therefore have therapeutic use as anti-cancer agents, as well as other therapeutic agents, for example, as anti-fertility agents as described following.